$-5lm + 5ln + l + 9 = 2m - 5$ Solve for $l$.
Combine constant terms on the right. $-5lm + 5ln + l + {9} = 2m - {5}$ $-5lm + 5ln + l = 2m - {14}$ Notice that all the terms on the left-hand side of the equation have $l$ in them. $-5{l}m + 5{l}n + 1{l} = 2m - 14$ Factor out the $l$ ${l} \cdot \left( -5m + 5n + 1 \right) = 2m - 14$ Isolate the $l$ $l \cdot \left( -{5m + 5n + 1} \right) = 2m - 14$ $l = \dfrac{ 2m - 14 }{ -{5m + 5n + 1} }$